1. FieId of the Invention
The present invention relates to a circuit for PCM conversion of an analog signal, such as a voice signal, with improvement of gain-tracking.
2. Prior Art
In recent years PCM (Pulse Code Modulation) coding has become very widespread, until it has become the modulation method most used in telephone systems. Among the various international recommendations (such as CCITT in Europe) which set rules on every possible telephone connection, those related to the PCM converter (normally constituted by an integrated circuit known as "Combochip") prescribe, among other things, a mask (described hereinafter) for limiting the gain error (i.e. gain-tracking) as the level of the input signal, assumed sinusoidal, varies.
Analog-digital conversion is performed with a quantizer which forces the analog signal to assume only preset discrete values, and with a sampler which samples the quantized signal and feeds the successive samples to an encoder. Since analog-digital conversion introduces, as is known, a quantization error in the signal to be encoded, this reflects in a corresponding error in the encoded signal, equivalent to a gain error, even for an ideal "combochip".